Following burn injury and subsequent bacterial wound contamination many patients develop metabolic and immunologic abnormalities, and multiple organ system failure. The central hypothesis is that burn injury triggers host mediator systems that lead to inflammatory self destruction. Recent preliminary data demonstrate that activated platelets enhance the inflammatory response of monocytes resulting in the amplification of two proinflammatory cytokines, interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFa). The interaction is a multistep process including (at least) a platelet associated IL-1 like factor, adhesive proteins expressed by activated platelets and important for docking, and platelet membrane associated factors necessary for priming of the monocyte-cytokine response. These studies will first focus on defining the molecular nature of the platelet associated IL-1 like molecule since preliminary studies show that 66 percent of the amplification can be blocked with IL-1 receptor antagonist. Cytokine specific neutralizing antibodies will be used to identify the factor, and the factor will be purified by immunoprecipitation. The role of platelet and monocyte adhesive proteins will also be studied using antibodies to P-selectin, thrombospondin, and GPIIb-IIIa. Furthermore, FACS analysis and electron microscopy will be used to observe the distribution of these adhesive proteins on activated platelets and PBMCs of burn patients. The role of activated platelets priming cytokine mRNA in monocytes will be evaluated using semiquantitative PCR. Long range goals are to define the role of the activated platelet in magnifying the monocyte-cytokine response in burn injury.